MICRON-SIZED DUST PARTICLES DETECTED IN THE OUTER SOLAR-SYSTEM BY THEVOYAGER 1 AND 2 PLASMA-WAVE INSTRUMENTS

During the Voyager 1 and 2 flybys of the outer planets it has been dem onstrated that the plasma wave instrument can detect small dust partic les striking the spacecraft. In this paper, we examine the Voyager pla sma wave data for dust impacts in the interplanetary medium at helioce ntric radial distances ranging from 6 to 60 astronomical units (AU). T he results show that a small but persistent level of dust impacts exis ts out to at least 30 to 50 AU. The average number density of these pa rticles is about 2 x 10(-8) m(-3), and the average mass of the impacti ng particles is believed to be a few times 10(-11) g, which correspond s to particle diameters in the micron range. Possible sources of these particles are planets, moons, asteroids, comets, and the interstellar medium. Of these, comets appear to be the most likely source. The num ber densities are only weakly dependent on ecliptic latitude, which in dicates that the particles probably do not originate from planets, moo ns, or asteroids. Comparisons with interstellar dust fluxes measured i n the inner regions of the solar system by the Ulysses spacecraft indi cate that the particles are not of interstellar origin.